12 or higher mol alkali metal hydroxide-1 mol sodium hydroxide reaction product,depilatories and depilation therewith



United States Patent 3,421,832 12 OR HIGHER MOL ALKALI METAL HYDROX- IDE-l MOL SODIUM HYDROXIDE REACTION PRODUCT, DEPILATORIES AND DEPILATION THEREWITH Alfred G. Minklei, Kenmore, Theodore H. Dexter, Lewiston, and James S. Sconce, Niagara Falls, N.Y., and Thomas C. Thorstensen, Chelmsford, Mass., assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed May 27, 1964, Ser. No. 370,702 US. Cl. 8-94.16 30 Claims Int. Cl. C14c 1/06 ABSTRACT OF THE DISCLOSURE Depilatories are made by reacting 12 mols or more of NaOH with phosphorus pentasulfide. Part of the alkali can be replaced by alkali metal sulfides and/or supplemented by calcium chloride as a sharpener.

This invention relates to improvements in the processing of animal hides into leather and more particularly relates to improved composition and methods for the unhairing of hides during such processing.

In the unhairing of animal hides in the course of processing the hides into leather, it is the practice to subject the hides to the action of some material which loosens the hair on the hide so that it may be easily removed. Although, from the standpoint of efiiciency of operation and utilization of processing equipment, it is desirable that the unhairing operation be carried out as rapidly as possible, it is also desirable that the materials used for this unhairing do not have appreciable deleterious effects on either the hide itself or on the hair which is removed. The reason for avoiding destruction of the latter is that the hair is a valuable by-product which is desirably recovered and sold. The reason for avoiding destruction of the former is, of course, obvious.

In the past, the unhairing of the hides has often been carried out by prolonged contact of the hides with a saturated lime solution containing excess solid lime. While this method is effective in removing the hair from the hides, without excessive damage to either the hide or the hair, the process is often time consuming, frequently requiring two to three days or longer to complete the unhairing operation. Accordingly, it is heretofore been proposed to add other reagents to the lime solution or slurry in order to speed up the unhairing operation. Exemplary of materials which have been used for this purpose include various sulfides, such as arensic sulfide, sodium sulfide, sodium sulfhydrate, and the like. Although such materials often do effect a material reduction in the time required to unhair, care must generally be exercised in the use of these materials so as to prevent damage to the hair. In this regard, it has been found that where even slight excesses of these materials are added to the lime solution or slurry, appreciable hair damage may result.

In a copending application, S.N. 241,132, filed Nov. 30, 1962, now Patent No. 3,365,265 a new and novel concept of unhairing compositions and methods are disclosed. In these unhairing processes, the unhairing is effected by utilizing a composition comprising a compound containing phosphorus and sulfur which compound, it is believed in the unhairing process, provides a controlled release of sulfhydrate ions in the unhairing solution. In this manner, an excess of sulfhydrate in the unhairing solution is avoided, which excess, has in the past, resulted in damage to or even complete destruction of the hair. Moreover, the presence of this controlled amount of sulf- 3,421,832 Patented Jan. 14, 1969 hydrate in the unhairing solution markedly increases the unhairing action of the solution and thus reduces the time required to effect substantially complete unhairing. Within this broad generic class of phosphorus and sulfur containing compounds suitable for use in the unhairing of animal hides and/or skins, it has now been found that a more specific and novel group of phosphorus and sulfurcontaining compositions provide unexpectedly beneficial results not only in terms of the speed at which unhairing is effected and the excellent condition of both the hair and the hides, but also in terms of maintenance of desired pH levels, as well as the ease of handling these materials and the wide range of concentrations in which they may safely be used to obtain these beneficial effects.

It is, therefore, an object of the present invention to provide a novel phosphorus and sulfur-containing composition, which composition is useful in the unhairing of animal hides and/ or skins.

Another object of the present invention is to provide a novel phosphorus and sulfur-containing composition which may be used for the unhairing of animal hides in either a conventional lime system or in a non-lime system.

A further object of the present invention is to provide an improved method for the unhairing of animal hides and/or skins, which method may be carried out easily and quickly and without damage to either the hides or the hair in either a lime or a non-lime system.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

Pursuant to the above objects, the present invention includes a composition, useful in unhairing animal hides and/or skins, which composition comprises an alkaline phosphorus-sulfur reaction product produced by reacting an inorganic phospho-sulfur compound with a liquid alkali metal hydroxide, in a mole ratio of more than about 12 moles of alkali metal hydroxide to one mole of inorganic phospho-sulfur compound expressed as P 8 to obtain a free alkali-containing product which is stable in aqueous solution at degrees centigrade. Aqueous solutions of these reaction products, both with and without lime, have been found to be extremely effective for removing hair from animal hides and skins. Not only is hair removal substantially complete when using these solutions but, additionally, the hair removed is substantially undamaged and because of this excellent condition is readily saleable at a top price. Preferably, for ease in handling, when used in formulating solutions for unhairing animal hides and skins, the novel compositions of the present invention are recovered as solids.

It is to be appreciated that in referring to a mole ratio of alkali metal hydroxide to inorganic phospho-sulfur compound of more than 12:1, the amount in excess may be quite small and need only be sufiicient to provide the free alkali in the product. Moreover, it will be understood that in establishing the mole ratio, the phospho-sulfur compound is expressed as P 5 and that this will be based on the phosphorus content of P 8 since this is the portion of the material which enters into the reaction with the alkali metal hydroxide.

More specifically, the alkali metal hydroxide used in formultaing the novel alkaline phosphorus-sulfur reaction products of the present invention is preferably sodium hydroxide. Other alkali metal hydroxides, i.e., potassium hydroxide, lithium hydroxide, cesium hydroxide, and rubidium hydroxide, may also be used with comparable results. Since it is the preferred alkali metal hydroxide, primary reference will be made hereinafter to sodium hydroxide. This is not, however, to be taken as a limitation on the alkali metal hydroxide which may be used but merely as being exemplary of these materials.

Moreover, it is to be understood that in referring to liquid alkali metal hydroxides it is intended to include both aqueous solutions as well as melts of alkali metal hydroxides.

Since, as has been indicated hereinabove, the novel alkaline phosphorus-sulfur containing reaction products of the present invention are preferably obtained as solids when they are to be used as unhairing agents, the water content of the sodium hydroxide used in their preparation is desirably maintained at a minimum. Thus, sodium hydroxide solutions containing at least about 50% sodium hydroxide are typical, with solutions of 70 percent or more sodium hydroxide being preferred. Additionally, alkali metal hydroxide solutions having a concentration below about 50 percent may also be used, as for example, solutions containing 10 percent or less sodium hydroxide by weight of the solution. It will be appreciated, of course, that where such less concentrated alkali metal hydroxide solutions are used, and it is still desired to obtain a solid product, appreciably larger quantities of water will have to be removed from the reaction mixture in order to obtain such desired solid product.

In this respect, with regard to the removal of the water from the reaction mixture in preparing a solid product, it is important that the water be removed from the reaction mixture, as for example, by evaporation, rather than removing the solid product from the reaction mixture, as for example, by crystallization. It is to be further understood, that this water removal from the reaction product may be effected either before, during, or after the reaction of the alkali metal hydroxide and the inorganic phospho-sulfur compound in the desired mole ratio. Thus, the reaction may be carried out at a sufiiciently high temperature so that water is continuously evaporated from the reaction mixture or, after the reaction is substantially complete, the reaction product may be heated to a sufficiently high temperature as to evaporate water therefrom. In each instance, the amount of water removed is sufiicient so that upon cooling the material to substantially room temperature, a solid product is obtained. As a further alternative, the removal of water may be effected prior to the reaction by using as a reactant a liquid alkali metal hydroxide solution which is highly concentrated. For example, when using a 70 percent solution of sodium hydroxide, which material is normally solid at room temperatures, no further removal of water from the reaction product is necessary in order to obtain a solid reaction product upon cooling the material to room temperature. Thus, in many instances, the most preferred sodium hydroxide solution for use in preparing the novel alkaline phosphorus-sulfur containing reaction products of the present invention, is a solution having a sodium hydroxide content of about 70 percent by weight.

Additionally it is desirable in the preparation of the compositions of the present invention that they contain excess alkali, e.g., NaOH, so as to obtain a more stable product. Accordingly, it is preferred that the inorganic phospho-sulfur compound be added to the alkali metal hydroxide, rather than vice versa. In this manner the desired excess of alkali is maintained even during the preparation of the compositions.

Considering now the inorganic phospho-sulfur compound which is reacted with the liquid alkali metal hydroxide in forming the novel compounds of the present invention, various inorganic phospho-sulfur compounds have been found to be suitable. Generally, it is found to be preferable that the molar ratio of sulfur to phosphorus in the inorganic phospho-sulfur compound used is not appreciably less than about :2. It is known that in some instances, inorganic phospho-sulfur compound having lower sulfur to phosphorus ratios, e.g., P 5 may hydrolyze to form phosphine. In view of the poisonous nature of this material, its formation is desirably avoided and for this reason, the use of inorganic phospho-sulfur compounds which have a sufficiently high sulfur to phosphorus ratio so as not normally to hydrolyze and form phosphine are preferred in preparing the novel compounds of the present invention. Exemplary of typical inorganic phospho-sulfur compounds, having the preferred phosphorus to sulfur ratios, which may be used are those materials falling within the range of about P 5 to about P 8 Of the various inorganic phospho-sulfur compounds falling with this range, the preferred material is phosphorus pentasulfide, P 8 or P 8 Accordingly, primary reference will be made hereinafter to phosphorus pentasulfide as being the preferred inorganic phospho-sulfur compound for use in forming the novel compositions of the present invention. This is not, however, to be taken as a limitation on the inorganic phospho-sulfur compound which may be used but merely as being exemplary of these materials.

As has been noted hereinabove, the sodium hydroxide and the phosphorus pentasulfied are reacted in amounts so as to provide a molar ratio of more than 12 moles of sodium hydroxide to one mole of phosphorus pentasulfide. It will be appreciated, that in forming the novel alkaline phosphorus-sulfur containing reaction products of the present invention, a portion of the sodium hydroxide used in the reaction mixture may be replaced by an alkali metal sulfide, such as sodium sulfide. Other alkali metal sulfides which may be used include potassium sulfide, lithium sulfide, and the like. By replacing the sodium hydroxide with an equivalent amount of sodium sulfide, it is meant that the amount of sodium sulfide used will provide, in the reaction mixture, sodium in an amount equal to that in the sodium hydroxide which is replaced. Thus, for example, since there are two moles of sodium in each mole of sodium sulfide, in a reaction mixture containing 14 moles of sodium hydroxide to one mole of phosphorus pentasulfide, two moles of the sodium hydroxide will be replaced by one mole of the sodium sulfide to give a reaction mixture containing 12 moles of sodium hydroxide, one mole of sodium sulfide, and one mole of phosphorus pentasulfide.

Where the novel compounds of the present invention are to be used in the unhairing of animal hides and/or skins, it is desirable that the amount of alkali metal sulfide which replaces sodium hydroxide in the reaction mix is limited to an amount which is less than that which will provide half as many sodium ions as are provided by the amount of sodium hydroxide remaining in the reaction mixture. For example, where the initial reaction mixture, before replacement of caustic soda with sodium sulfide, contains 18 moles of caustic soda to 1 mole of P 5 no more than 6 moles of the caustic soda should be replaced by the equivalent 3 moles of sodium sulfide. In this manner, the final reaction mixture will contain 12 moles of caustic soda, three moles of sodium sulfide and 1 mole of P 8 and will have twelve moles of sodium supplied by the caustic soda and six moles of sodium supplied by sodium sulfide. In some instances, it may be desirable that no more than about 4 moles of caustic soda be replaced by alkali metal sulfide. It has been found that as greater amounts of the alkali metal hydroxide are replaced by the sodium sulfide, and the resulting reaction product is used in the unhairing of animal hides and/or skins, the amount of damage to the hair which is removed may also increase and may, thus, detract from the desirability of using this product in such processes. It is for this reason that it is preferred to limit the amount of sodium hydroxide which is replaced by sodium sulfide in the reaction to the amount which has been indicated hereinabove.

It will be appreciated that, if desired, various sulfurcontaining materials may also be added to the novel phosphorus-sulfur containing reaction products of the present invention to provide an added sharpening effect for unhairing. Preferably, these materials are blended into the novel compositions of the present invention after they are prepared, although in some instances they may be combined with the initial reactants used in preparing these phosphorus-sulfur containing reaction products. Exemplary of sulfur materials which may be used are sulfur, alkali metal sulfides, alkali metal sulfhydrates, and the like. Typically, these materials will be present in amounts up to about percent by weight of the inorganic phosphosulfur compounds, with amounts within the range of about 1 to about 10 percent being preferred.

In preparing the novel alkaline phosphorus-sulfur containing reaction products of the present invention, the mole ratio of alkali metal hydroxide to inorganic phosphosulfur compound is more than 12: 1. Where these compositions are to be used in a conventional lime system for unhairing animal hides or skins, it is preferred that the mole ratio of sodium hydroxide to phosphorus pentasulfide used in preparing the compounds is not greater than about :1, with mole ratios of about 14:1 to about 16:1 being specifically preferred. It has been found that novel alkaline phosphorus-sulfur containing reaction products of the present invention prepared using appreciably higher ratios of alkali metal hydroxide to phosphorus sulfide material than 20: 1, for example, ratios of 50 to 60:1 or even higher will generally give excellent unhairing without appreciable damage to the hair. When using such higher ratio materials in a conventional lime system, however, the added alkalinity provided by such materials may result in undesirable swelling or plumping of the hide which, in some instances may have an adverse effect on the leather ultimately produced. Accordingly, it is for this reason that the lower ratio materials, e.g., those having a sodium hydroxide to P 5 ratio not substantially in excess of about 20: 1, are preferred for effecting unhairing of hides or skins in a conventional lime system and not because such higher ratio materials do not provide effective unhairing.

In referring to a conventional lime system for unhairing, it is believed that those in the art will understand this to mean a system wherein a solution or slurry of lime is used. Typically, the lime slurry used may contain about 6 percent of lime, based on the total soaked or wet weight of the hides to be unhaired. This amount of lime, of course, includes both the lime which is in solution and that which remains in the solid state, suspended in the solution. Obviously, as is known to those in the art, lime slurries or solutions containing greater or lesser amounts of lime may also be used.

To a lime solution or slurry, as described above, the novel alkaline phosphorus-sulfur containing reaction product of the present invention is added. Preferably such compositions are prepared by the reaction of an alkali metal hydroxide and an inorganic phospho-sulfur compound in a mole ratio within the range of about 12:1 to about 20:1 and includes also those compositions wherein a portion of the sodium hydroxide has been replaced by an alkali metal sulfide in the reaction mixture, as described above. The phosphorus-sulfur containing reaction product of the present invention is added to the lime solution or slurry in an unhairing amount, i.e., an amount which is effective in promoting the unhairing of animal hides and skins in a relatively short time without excessive damage to the hair removed. Typically, the amounts of the reaction product added will be within the range of about 0.1 to about 10 percent by weight of the hides or skins being treated. It will be appreciated, however, that depending upon the total alkalinity of the phosphorus-sulfur containing reaction product added, its sulfur content and the like, greater and lesser amounts of the material may be used to obtain rapid unhairing with substantially no hair damage. In many instances it has been found that excellent results are produced by using the novel alkaline phosphorus-sulfur containing reaction products in amounts within the range of about 1 to about 4 percent by weight of the hides being treated.

In addition to conventional lime systems for unhairing animal hides and skins, considerable attention has been given recently to the use of so-called non-lime systems. Such systems have become increasingly important in view of more stringent governmental regulations relating to the disposal of tannery effluent materials, since with such nonlime systems there are no substantial amounts of suspended solids in the effluent. As has been indicated hereinabove, the novel alkaline phosphorus-sulfur containing reaction products of the present invention have also been found to be extremely effective in unhairing animal hides or skins without substantial damage to the hair in nonlime systems.

In these non-lime systems, the necessary alkalinity, i.e., alkalinity sufficient to effect unhairing is provided by a compound which, in aqueous solution, produces sufficient hydroxyl ions to provide the needed alkalinity. Suitable compounds for this purpose include the alkali metal hydroxides, e.g., sodium, potassium, lithium, cesium, and rubidium hydroxides, as well as ammonium hydroxide, amines, urea, ammonia, and the like. Additionally, the non-lime systems may contain a source of calcium ions, as a sharpening agent, the amount of such calcium ions source being such that the amount of calcium ions provided is not sufficient to form a substantial amount of a calcium-containing precipitate in the solution. Suitable calcium materials which may be used include the more soluble calcium salts, such as calcium chloride, calcium nitrate and the like. It will be appreciated that sharpening agents, other than calcium materials may also be used. These are known to those in the art and include the alkali metal sulfhydrates, alkali metal carbonates, hydrosulfites, such as zinc hydrosulfite, as well as compounds of alkaline earths other than calcium, such as barium, strontium and the like. As with the calcium materials, the more soluble salts, e.g., chlorides, nitrates, sulfates, and the like are preferred. It may also be desirable to include in the composition an inert salt which, in solution provides a buffering action on the system, i.e., acts in some manner to temper the alkalinity and decrease swelling. Suitable inert salts include the alkali metal halides, e.g., sodium chloride, alkali metal nitrates, alkali metal sulfates, and the like. In general, it is desirable that unhairing solutions, both lime and non-lime, have sufficient alkalinity so as to have pH of at least about 12 and preferably within the range of about 12.2 to about 12.8. Desirably, the pH of the unhairing solution is not substantially in excess of about 13, since at such higher pH values, hair damage may occur.

It will be appreciated that in effecting unhairing of hides and skins in a non-lime system, the novel phosphorussulfur containing reaction products of the present invention, prepared from a reaction mix containing the preferred sodium hydroxide to phosphorus pentasulfide ratios of from at least 12:1 to about 20:1 may be added to an alkaline solution containing sufficient alkaline material, e.g., sodium hydroxide, to provide the alkalinity to effect unhairing. Such alkaline solutions will also, generallly contain sharpening agents such as a calcium materials, with calcium chloride being preferred, and may also contain an inert salt such as sodium chloride in the amounts as have been indicated hereinabove. Alternatively, the alkaline material needed to provide the alkalinity for carrying out the unhairing may be incorporated in the novel phosphorus-sulfur containing reaction products of the present invention by utilizing higher ratios of alkali metal hydroxide to inorganic phospho-sulfur compound in preparing these compositions. For example, molar ratios of sodium hydroxide to phosphorus pentasulfide of about 40:1, and preferably about 48:1, or even higher, e.g., 55 to 60:1 may be used. For unhairing, such compositions may then be formed into an aqueous solution to which is added the sharpening material, e.g., the calcium material, and the inert salt in the amounts desired. If desired, however, a solid composition containing all of these components may be formulated by adding to the phosphorus-sulfur containing reaction product reaction product the calcium chloride and, if desired, the sodium chloride, in amounts such that when the resulting composition is dissolved in water, the resulting aqueous solution will contain the requisite amounts of calcium ion, inert salt,

phosphorus-sulfur containing reaction product and have sufiicient alkalinity to effect rapid and substantially complete unhairing of the animal hides or skins. While it is possible that the sharpening agent as well as the inert salt may be added to the reaction mixture during the preparation of the phosphorus-sulfur containing reaction product, it is generally preferred that these materials, i.e., calcium chloride and sodium chloride are dry blended with the novel phosphorus-sulfur composition of the present invention after its preparation. In this manner, there is obtained a product which is relatively easily handled and formulated into an aqueous unhairing solution. Obviously, of course, only the sharpening agent, e.g., calcium chloride, or the inert salt, e.g., sodium chloride, may be combined with the phosphorus-sulfur containing reaction product and the other may be added separately to the subsequently formed unhairing solution as it is needed. Typical of compositions which may be used, is one formed by the reaction of sodium hydroxide and phosphorus pentasulfide, as has been described hereinabove, in a molar ratio of 48 moles of caustic soda to 1 mole of P 5 the thus-obtained solid reaction product then being dry blended with 7.8 moles of calcium chloride.

In general in formulating the non-lime systems, these will preferably contain the hydroxyl ion source in an amount within the range of about 0.5 to about 50 percent by weight the sharpening agent, such as the calcium ion source, in an amount within the range of about 0.1 to about 10 percent by weight, the novel phosphorus-sulfur containing reaction product of the present invention in an amount within the range of about 0.1 to about 10 percent by weight, and the inert salt in an amount within the range of about 0.5 to about 50 percent by weight, all of the above amounts being percent by weight of the hides to be unhaired. Preferably, such non-lime unhairing systems will contain the hydroxyl ion source, such as sodium hydroxide, in an amount within the range of about 3 to percent by weight, the sharpening agent, such as calcium chloride, in an amount within the range of about 1 to about 4 percent by weight, the novel phosphorussulfur containing reaction products, such as one prepared by reacting caustic soda and P 8 in a mole ratio of about 16:1, in an amount within the range of about 1 to about 4 percent by weight, and the inert salt, such as sodium chloride, in an amount within the range of about 3 to about 20 percent by weight. It will be appreciated that where the non-lime system is prepared .by forming an aqueous solution of a composition containing the hydroxyl ion source, the sharpening agent and the inorganic phospho-sulfur compound, such as the above-described composition containing 48 moles of sodium hydroxide, 7.8 moles of calcium chloride and 1 mole of phosphorus pentasulfide, such compositions are typically dissolved in water in amounts within the range of about 0.3 to about percent by weight of the hides to be unhaired, and preferably in amounts within the range of about 3 to about 12 percent by weight of the hides. To such solutions, the inert salts, such as sodium chloride, may then be added in the desired amounts as have been described above.

In effecting the unhairing of animal hides or skins utilizing the compositions of the present invention, a conventional lime system is formulated with a solution or slurry of lime and the novel phosphorus-sulfur containing reaction products of the present invention, as described hereinabove, or a nonlime system is used, formulated in the manner which has heretofore been described. The unhairing solutions used may also contain, if desired, small amounts of additional sharpening agents, such as the alkali metal sulfides, alkali metal sulfhydrates, alkali metal tetrasulfides, and the like. Where such materials are added to the unhairing solution, they are generally present in amounts up to about 2 percent by weight of the hides to be unhaired, amounts of about 0.1 to about 0.5 percent being typical.

Preferably, prior to contacting the hides with the unhairing solution, the hides are subjected to a soaking operation, as is known in the art. Typically, such soaking operations are carried out utilizing Water as a soaking medium although, if desired, small amounts of alkali metal sulfides, tetrasulfides, sulfhydrates etc., may be added to the soaking water. Where such materials are added to the soaking water in amounts up to about 2 percent by weight of the hides being treated, they have been found to be beneficial in providing a preliminary loosening of the hair prior to the actual unhairing operation. The use of such sulfur containing additives in the soaking operation is, however, not essential to the operation of the present process.

The hides are maintained in the Soaking medium for a period of time sufficient to provide a thorough wetting of the hides, times of up to 24 hours being typical. Generally, sufficient quantities of soaking solution will be provided so as to float the hides, weight ratios of soaking solution to hides of about 4:1 being typical of those which may be used. The temperatures utilized in this soaking operation are, in general, not critical although at higher temperatures, the soaking may produced more rapidly. For convenience, however, the soaking operation is usually carried out at about room temperature, i.e., about degrees Fahrenheit, although higher or lower temperatures may be used with no adverse effects on the soaking operation. During the soaking, the hides or skins may be agitated or paddled, the frequency and amount of such agitation or paddling being determined by the practice normally followed in ordinary soaking procedures.

After completion of the soaking operation, the hides or skins are brought into contact with the unhairing solution. Generally, the contact of the hides in the unhairing solution is effected in a paddle or a drum, although, if desired, batch or still pits may be used. The temperature of the unhairing solution, i.e., the temperature at which the unhairing operation is carried out, is generally not critical, although the use of higher temperatures may shorten the time of the unhairing operation. Typically, the unhairing is at about room temeprature, e.g., about 70 degrees to degrees Fahrenheit, although higher and lower temperatures may be used. As in the soaking operation, sufiicient unhairing solution is utilized to effectively float the hides, a weight ratio of solution to hides of about 4:1 again being typical. The time required to effect substantial loosening of the hair on the hides will, of course, vary depending upon the nature of the hides, solution strength, temperature, and the like. Although times of 48 or more hours are not uncommon, in some instances periods of 18 to 24 hours may be sufiicient to effect substantially complete unhairing of the hides. During the time the hides are in contact with the unhairing solution, they may be agitated or paddled so as to effect a more intimate contact between the hides and the solution. The extent and nature of such paddlnig may vary in each instance, and will generally conform to the normal practices in the art. After removal of the hides or skins from the unhairing solution, they are passed through conventional unhairing equipment wherein substantially all of the hair, including the very fine hair is removed. It has been found that by the use of the above procedures, not only is substantially all of the hair removed from the hide, often in a period of time appreciably shorter than that which has been possible using the prior art unhairing compositions, but, additionally, the hair removed is found to be of excellent quality with substantially no damage to either the hair or the hide being experienced.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, the temperatures are given in degrees Fahrenheit, quantities are expressed in grams, and percentages are percent by weight of the hides being treated.

In 226 grams of water, 336 grams of sodium hydroxide were dissolved. To this soltuion was added 304 grams of phosphorus pentasulfide the rate of the addition being controlled only to the extent that violent boiling of the solution by the exothermic reaction taking place was avoided. After the addition of the P 8 was complete heating of the solution was continued until about 58 percent of the water had evaporated. The reaction mixture was then permitted to cool, hardening to a solid having a mole composition of 12 moles NaOH to 1 mole of P S This composition was found to contain 11.0 percent phosphorus, 28.83 percent sulfur, and 0.086 percent free alkali.

EXAMPLE 2 The procedure of Example 1 was repeated with the exception that 912 grams of phosphorus pentasulfide was added to a solution formed by dissolving 1008 grams of sodium hydroxide and 534 grams of 60 percent sodium sulfide in 678 grams of water. 51 percent of the water was evaporated by heating and the solution was cooled and allowed to harden. The resulting solid, cream colored product had a mole ratio of 12 moles NaOH to 2 moles Na S to 1 mole P 8 and contained 9.15 percent phosphorus, 27.15 percent sulfur and 10.8 percent free alkali.

EXAMPLE 3 The procedure of the preceding example was repeated with the exception that 152 grams of phosphorus pantasulfide was added to 271 grams of 85 percent potassium hydroxide and 90 grams of sodium sulfide, dissolved in 181 grams of water. After evaporation of water from the solution as in the preceding Example, the solid material recovered was found to have a mole composition of 12 moles of KOH to 2 moles Na s to one mole 'of P 8 EXAMPLE 4 The procedure of the preceding examples was repeated with the exception that 150 grams of P 5 was added to 220 grams of sodium hydroxide dissolved in 144 grams of water. After evaporation of water as in the preceding examples the solid material recovered was found to have a mole composition of 16 moles sodium hydroxide to 1 mole phosphorus pentasulfide.

EXAMPLE 5 The procedure of Example 4 was repeated with the exception that 50 grams of phosphorus pentasulfide was added to 110 grams of 85 percent potassium hydroxide dissolved in 64 grams of water. After evaporation of water from the solution, a solid product was recovered having a mole composition of 30 moles KOH to 1 mole P 5 EXAMPLE 6 152 grams of phosphorus pentasulfide was added to 1,312 grams of a 50 percent aqueous solution of sodium hydroxide. This mixture was then evaporated until sufficient water was removed so as to allow the solution to solidify upon cooling to room temperature. The resulting solid material was ground and 294 grams of calcium chloride was dry blended into it. The resulting product had a mole composition of 48 moles sodium hydroxide, 7.8 moles calcium chloride and 1 mole phosphorus pentasulfide.

The preparations of the preceding examples were repeated using other ratios of the alkali metal hydroxide to the inorganic phospho-sulfur compound, e.g., ratios of 18:1, 24:1, 30:1, and the like, using other alkali metal hydroxides, e.g. lithium hydroxide, using other inorganic phospho-sulfur compounds, e.g., P 8 and dry blending various sulfur materials, e.g. sulfur, sodium sulfide, sodium sulfhydrate, etc., with the reaction product of the alkali metal hydroxide and the phosphorus sulfide material. In

10 each instance, a solid product was obtained, comparable to that prepared in the preceding examples.

EXAMPLE 7 To illustrate the effectiveness of compositions prepared as described hereinabove in unhairing animal hides or skins, a quantity of hide pieces were soaked in water over night at a temperature of about 70 degrees Fahrenheit. The soaked hides were then divided into 500 gram sample quantities and each sample quantity was placed in 2000 milliliters of a lime slurry, containing 6 percent lime based on the weight of the soaked hides. Each of the lime slurries also contained 2 percent, based on the weight of the soaked hides, of a phosphorus-sulfur composition prepared in the manner as described in the preceding examples. The hide sample remained in the slurry for a period of 48 hours, with periodic agitation to insure a thorough wetting of the hides. The pH of the unhairing slurry during the 48 hour period in each of the test solutions was beaten 12.5 and 12.6, with substantially no change in pH over the entire 48 hour period. At the end of 48 hours, the hide samples were removed from the unhairing solutions and evaluated as to unhairing and hair condition, with the following results being obtained:

Hair conditio Composition used (mole ratio) Unhairing EXAMPLE 8 The procedure of the preceding example was repeated with the exception that other phosphorous-sulfur containing reaction products were used, in the lime slurry the hide samples were removed from the unhairing solution for evaluation after 24 hours, and that varying amounts of the phosphorus-sulfur compositions were used. Using this procedure, the results obtained were as follows:

Percent by wt. Composition used (mole ratio) (based on Unhairing Hair weight condition hides treated) 16Il%%:1P4S1o+7% NaSH 6 Very good Good.

a e 16KOH:1P4S1o+7% NaSH 8 do Do.

added. 16K0H:1P4Sw+7% S added Do. 16KOH:1P4Sm+7% S added Do. 16K0H:1P4Sm+7% S added Do. lfiKOHZ1P4S1o-I-7% Nags D0.

added. 16LlOHZ1P4sl0 D0. D0. Do. Do. D0. D0. Do. 2 .do D0. 4 Very good.-. D0.

EXAMPLE 9 A quantity of cattle hides were soaked in water over night as in Example 1. Thereafter, 500 gram sample quantities of the hides were placed in 2000 milliliters of water to which was added varying quantities of a phosphorussulfur reaction product composition to which had been added calcium chloride, Which composition was prepared in the manner set forth in Example 4. The mole composition of this material was 48 moles sodium hydroxide, 7.8 moles of calcium chloride and 1 mole of phosphorus pentasulfide. The hide samples were maintained in the solution for 24 hours with periodic agitation to insure thorough wetting of the hides. The initial pH of the solu- Concentration (percent hosed on Unhairing Hair condition weight of hides treated) EXAMPLE 10 The procedure of the previous example was repeated with the exception that in place of the phosphorus-sulfur composition used in that example, 2 percent, based on the weight of the hides, of a phosphorus-sulfur containing reaction product having a mole composition of 12 moles of sodium hydrxide to 1 mole of phosphorus pentasulfide was added to the water. Additionally, varying percentages of calcium chloride and sodium hydroxide, based on the weight of the hides were also added to the solution. The hide sample were maintained in the solution for 24 hours with periodic agitation. The initial pH was within the range of about 12.6 to about 12.7 and the final pH was within the range of about 12.6 to about 12.8, there being substantially no change in the pH over the 24 hour period. At the end of this time, the hides were removed from the solution and evaluated as to unhairing and hair condition with the following results:

CaClr NaOH Uuhairing Hair Concentration Concentration Condition 2. 29 Very good Good.

2.57 .do Do. 286 Do. 3.15 Do. 3.43 Do. 4.1 Do.

EXAMPLE 11 The procedure of Example 10 was repeated with the exception that the phosphorus-sulfur composition used had a mole composition of 16 moles KOH to 1 mole P 8 and was used at a concentration of 3 percent based on the weight of the hides being treated. Additionally, the concentration of the calcium chloride was maintained constant at 2 percent based on the weight of the hides and sodium chloride in an amount of percent based on the weight of the hides added to the solution. The percent of sodium hydroxide used was varied, the percentage used being based on the weight of the hides being treated. The evaluation of the hides for unhairing and hair condition after 24 hours in the solution gave the following results:

Hair

Unhairing condition NaOH concentration EXAMPLE 12 samples after the 24 hours, as to unhairing and condition gave the following results:

Composition used Amount used Unhairlug Hair (mole percent) in grams condition llNaOHzlhS 10.5 Good Good.

EXAMPLE 13 To 250 pounds of a 50 percent aqueous solution of sodium hydroxide was added 190 pounds of anhydrous flake sodium hydroxide. The resulting material had a sodium hydroxide concentration of about 70 percent. To this material was added 245 pounds of phosphorus pentasulfied over a period of about 5 hours, the reaction temperature during this time being within the range of about 110 to 125 degrees centigrade. When the addition of the phosphorus pentasulfide was completed the liquid product was discharged onto a drum type flaker and flaked to obtain about 700 pounds of a solid product. This product had a mole composition of about 14 moles sodium hydroxide to 1 mole phosphorus pentasulfide.

EXAMPLE 14 A pack of cow hides containing 173 sides and weighing 4200 pounds was soaked over night in a paddel in water at a temperature of about 74 degrees Fahrenheit, the weight ratio of water to hides being about 4:1. This soaking solution also contained 0.2 percent by weight of the hides of sodium tetrasulfide and 0.2 percent by weight of the hides of a germicide. After soaking over night, the hides were removed from the paddle and the soaking solution drained from the paddle. The hides were fleshed and returned to the paddle. Water was added to the paddle to provide a water ratio to hides of about 3 /2 to 1, the temperature of the hides and the water in the paddle being about degrees Fahrenheit. pounds of the phosphorus-sulfur containing composition prepared as in Example 13 was added to the paddle. This amount of the phosphorus-sulfur containing composition, which was 2 percent by weight of the hides, was added as a solution, formed by dissolving 85 pounds of the solid flaked material in 30 gallons of water. Thereafter, the paddle was run for about 2 minutes an allowed to rest for an hour. 250 pounds of hydrated lime, which was about 6 percent by weight of the hides, was then added to the paddle. The hides were then retained in this solution in the paddle for a total period of 44 hours, the paddle being run for periods of up to 5 minutes each hour during this time. During this time, it was noted that there was substantially no odor coming from the paddle, as compared to paddles containing the regular production unhairing solution, which utilized a lime slurry containing dimethylamine sulfate and sodium sulfide as the unhairing agent and evidence a strong amino-sulfide odor. At the end of the 44 hour period, the sides were taken from the paddle and run through a conventional unhairing machine. It was noted that in removing the hides from the paddle, there was still substantially no odor and it was easier and quicker to handle the hides as they were not as slippery as those from the regular production which utilized the lime slurry containing dimethylamine sulfate and sodium sulfide. After passing the hides through the unhairing machine, they were then given a conventional bating, after which the hides appeared to be very clean with substantially no evidence of scud, fine hair, or hair roots. The sides were then pickled in a conventional salt and sulfuric acid pickle and were then given a chrome tanning. Thereafter, the leather was sorted, shaved, retanned and compared to that obtained from the conventional unhairing system, as described above. It was noted that the leather produced using the novel compositions of the present invention for unhairing was at least equivalent to that obtained from the regular production runs. Moreover, the hair which had been removed from the sides treated with the composition of the present invention was inspected and evaluated as being of top quality as compared to the hair obtained from the regular production systems, which latter hair was evaluated as being of poor quality. This latter hair was also very dark in color, only about A to /2 as long as the hair removed using the compositions of the present invention, and appreciably weaker and less clean than that obtained with the present compositions.

While there have been described various embodiments of the invention the compositions and methods described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A composition comprising an alkaline phosphorussulfur containing reaction product produced by reacting an inorganic phospho-sul-fur compound with a liquid alkali metal hydroxide in a mole ratio of more than about 12 moles of alkali metal hydroxide to 1 mole of phosphorus sulfide, to obtain a free alkali containing product which is stable in aqueous solution at 100- degrees centigrade.

2. The composition as claimed in claim 1 wherein the alkali metal hydroxide is sodium hydroxide and the inorganic phospho-sulfur compound is a material from P4810 to F482;.

3. The composition as claimed in claim 2 wherein the inorganic phospho-sulfur compound is phosphorus pentasulfide.-

4. The composition as claimed in claim 1 wherein a portion of the alkali metal hydroxide is replaced by alkali metal sulfide, the amount of alkali metal sulfide being not substantially greater than the amount which will provide half as many alkali metal ions in the product as are provided by the alkali metal hydroxide remaining in the product.

5. The composition as claimed in claim 4 wherein the alkali metal sulfide is sodium sulfide.

6. The alkaline phosphorus-sulfur containing reaction product as claimed in claim 1 having a mole composition of from about 14 to about 16 moles of sodium hydroxide to one mole of phosphorus pentasulfide.

7. The composition as claimed in claim 1 wherein, in addition to the reaction product of the alkali metal hydroxide and the inorganic phospho-sulfur compound, there is also contained a sharpening agent.

8. The composition as claimed in claim 7 wherein the sharpening agent is calcium chloride.

9. The composition as claimed in claim 8 having a mole composition of 48 moles sodium hydroxide, 7.8 moles of calcium chloride and 1 mole phosphorus pentasulfide.

10. A method of preparing an alkaline phosphorussulfur reaction product which comprises reacting an inorganic phospho-sulfur compound with a liquid alkali metal hydroxide in a mole ratio of more than about 12 moles of alkali metal hydroxide to one mole of inorganic phospho-sulfur compound and obtaining a free alkali containing product which is stable in an aqueous solution at 100 degrees centigrade.

11. The method as claimed in claim 10 wherein the liquid alkali metal hydroxide is an aqueous solution of sodium hydroxide and the inorganic phospho-sulfur compound is within the range of P 8 to P 8 12. The method as claimed in claim 11 wherein the 14 inorganic phospho-sulfur compound is phosphorus pentasulfide.

13. The method as claimed in claim 12 wherein the aqueous sodium hydroxide solution contains about 70 percent sodium hydroxide and is present in an amount within the range of about 14 to about 16 moles of sodium hydroxide to one mole of phosphorus pentasulfide and there is obtained a solid reaction product by cooling the reaction mixture.

14. A method of preparing an alkaline phosphorussulfur reaction product which comprises reacting an aqueous solution of sodium hydroxide with phosphorus pentasulfide in a mole ratio of more than about 12 moles of sodium hydroxide to 1 mole of phosphorus pentasulfide, removing sufficient water from the reaction mixture so that a solid product is obtained upon cooling the mixture, and cooling the reaction mixture to obtain a solid, free alkali containing product which is stable in aqueous solution at degrees centigrade.

15. The method as claimed in claim 10 wherein a portion of the alkali metal hydroxide in the reaction mixture is replaced with an alkali metal sulfide, the amount of alkali metal sulfide being not substantially in excess of that which will provide half as many alkali metal ions in the reaction mixture as are provided by the alkali metal hydroxide remaining in the reaction mixture.

16. The method as claimed in claim 15 wherein the alkali metal sulfide is sodium sulfide.

17. A composition for unhairing animal hides and skins which comprises an aqueous solution having a pH of at least about 12 and containing an unhairin-g amount of an alkaline phosphorus-sulfur the reaction product produced by reacting an inorganic phospho-sulfur compound with a liquid alkali metal hydroxide in a mole ratio of more than about 12 moles of alkali metal hydroxide to One mole of inorganic phospho-sulfur compound to obtain a free alkali containing product which is stable in aqueous solution at 100 degrees centigrade.

18. The composition as claimed in claim 17 wherein the phosphorus-sulfur containing reaction product has a mole composition of from about 12 to about 20' moles of alkali metal hydroxide to one mole of phosphorus pentasulfide.

19. The composition as claimed in claim 18 wherein the mole composition is from 14 to about 16 moles of sodium hydroxide to one mole of phosphorus pentasulfide.

20. A composition for unhairing animal hides and skins which comprises an aqueous slurry of lime and an unhairin-g amount of an alkaline phosphorus-sulfur containing reaction product produced by reacting an inorganic phospho-sulfur compound with a liquid alkali metal hydroxide in a mole ratio of more than about 12 moles of alkali metal hydroxide to one mole of inorganic phospho-sulfur compound to obtain a free alkali containing product which is stable in aqueous solution at 100 degrees centigrade, which composition has a pH within the range of about 12 to about 13.

21. A composition for unhairing animal hides and skins which comprises an aqueous solution containing an unhairing amount of an alkaline phosphorus-sulfur containing reaction product produced by reacting an inorganic phospho-sulfur compound with a liquid alkali metal hydroxide in a mole ratio of more than about 12 moles of alkali metal hydroxide to one mole of inorganic phospho-sulfur compound to obtain a free alkali containing product which is stable in aqueous solution at 100 degrees centigrade, a source of hydroxyl ions and a sharpening agent, the hydroxyl ion source being present in an amount to provide sufiicient alkalinity to maintain the solution at a pH within the range of about 12 to about 13.

22. The composition as claimed in claim 21 wherein the sharpening agent is a calcium ion source and the hydroxyl ion source and the calcium ion source are 15 combined with the alkaline phosphorus-sulfur containing reaction product, which composition is dissolved in water to form the aqueous unhairing composition.

23. The composition as claimed in claim 22 wherein the alkaline phosphorus-sulfur containing reaction product has a mole composition of 48 moles of sodium hydroxide, 7.8 moles of calcium chloride and 1 mole of phosphorus pentasulfide.

24. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 17 for a sufiicient period of time to etfect substantially complete loosening of the hair thereon.

25. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 18 for a sufficient period of time to effect substantially complete loosening of the hair thereon.

26. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 19 for a sufiicient period of time to effect substantially complete loosening of the hair thereon.

27. A method of unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 20 for a sufiicient period of time to effect substantially complete loosening of the hair thereon.

28. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 21 16 for a sufficient period of time to effect substantially complete loosening of the hair thereon.

29. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 22 for a sufiicient period of time to effect substantially complete loosening of the hair thereon.

30. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with the unhairing composition of claim 23 for a sufficient period of time to effect substantially complete loosening of the hair thereon.

References Cited UNITED STATES PATENTS 2,033,913 3/1936 Fiske et al. 894 2,067,628 1/1937 Fiske et al. 8-94 2,229,420 1/1941 Neugebauer 8--94.16

FOREIGN PATENTS 29,989 1910 Great Britain. 378,425 8/ 1907 France.

OTHER REFERENCES PMatthews: Application of Dyestuffs, pp. 72, 74, 89, 117 and 118, pub. 1920, John Wiley and Sons, N.Y.C.

Wilson: The Chemistry of Leather Manufacture, pp. 266-270, pub. 1928, The Chemical Catalog C0., N.Y.C.

NORMAN G. TORCHIN, Primary Examiner.

D. LEVY, Assistant Examiner. 

